Air swept pulverizer having an eccentrically arranged air throat flow area



March 13, 1951 G. w. BICE' 2,545,254

AIR SWEPT PULVERIZER WITH AN ECCENTRICALLY ARRANGED AIR THROAT FLOW AREA 3 Sheets-Sheet 1 Filed June 20, 1945 INVENTOR- Gra/mm WB/ce ATTORN EY March 13, 1951 w E 2,545,254

G. AIR SWEPT PULVERIZER WITH AN ECCENTRICALLY ARRANGED AIR THROAT FLOW AREA Filed June 20, 1945 5 Sheets-Sheet 2 INVENTOR gi/lam WB/ce ATTORNEY March 13, 1951 AIR s PT PULVER INVENTOR' Graham WB/ce ATTORNEY Patented Mar. 13, 1951 AIR SWEPT PULVERIZER HAVING AN EC- CENTRICALLY ARRANGED AIR THROAT FLOW AREA Graham W. Bice, Rosemontjla assignor to The Babcock & Wilcox Company, Rockieigh, N. J., a corporation of New Jersey Application June 20, 1945, Serial No. 600,531

6 Claims (01. 24160) The present invention relates'to' the construction and operation of pulverizers of the type in which materials, such as coal, rock, and the like, are pulverized between one or more grinding surfaces and a relatively moving rolling grinding element or elements and the pulverized material carried out of the grinding zone in suspension in a gaseous carrier medium. A pulverizer of this general type is shown in U. S. Patent No. 2,275,- 595, in which the pulverizing elements are relatively movable upper and lower grinding rings between which a circular .row of grinding balls is horizontally arranged and the pulverized material removed from the grinding zone by a stream of carrier air passing upwardly through an annular throat and picking up pulverized material discharged from the outer circumferentialedge of the lower grinding ring.

In the operation of such pulverizers air or other gaseous medium used for the classification of pulverized materials within the pulverizer is customarily used as a carrier medium to transport the finely divided product discharged from the pulverizer to points of use or storage. When the material pulverized is coal or other solid fuel the carrier air is also, used-as primary combustion air in burning the fuel. Since, inthe useof pulverizers of this type, particularly .in direct fir: ing installations, the capacity of the pulverizer may be varied over a wide range to accommodate the fuel requirements of the furnace served, it is also customary to change the rateof air flowpro portionately or in predetermined ratio withthe fuel rates delivered to the furnace. Such changes in air flow will also change the velocity of the air passing through the annular throat adjacent the discharge edge of the lower grinding ring and if the velocity is less than a definite critical value it will permit a dribble of materials, downwardly through the throat against the ascending stream of air. While it is desirable to permit a dribble of materials having a specific gravity greater than that of coal through the throat, such as for example, particles of pyrities, slate, tramp iron and the like, any loss of fuel by dribble through the throat should be avoided.

In the construction of pulverizers of the type described, the pulverizer air inlet is usually arranged for radial air delivery into an annular air chamber surrounding the throat and adapted to direct the fiow of air into the lower end of the throat passage. Other pulverizer arrangements have introduced air into the air chamber at positions other than radial to the pulverizer, but in all constructions the problem has been to arrange the air introduction so as to provide a substantially uniform allocation of air passing through each equal segment of throat throughout the circumference of the pulverizer.

With an unequal airflow velocity through different circumferential portions of the throat the minimum air flow through the pulverizer is limited to thecritical flow velocity of air through that segment of throat having the least flow velocity of air. Such an unbalance condition of air flow through the various segments of the throat will not only limit the air flow range of the pulverizer, but may also increase the dribble through the throat particularly at low capacities. In addition, such conditions may adversely affect the efiectiveness of size classification within the pulverizer and cause non-uniformity in the combustibility of the air-coal mixture discharged through the individual multiple pulverizer out lets to separate furnace burners.

The principal object of the present invention is to provide a pulverizer of the type described which is characterized by an improved construction and arrangement of the parts forming the air throat of a pulverizer. A further and more specific object is to provide an improved pulverizer throat whereinthe velocity and pressure of the air leaving the air throat adjacent the grinding zone of the pulverizer is substantially uniform for each segment throughout the circumference of the throat. An additional object is to provide a pulverizer throat construction which will permit a substantially uniform quantitative and qualitative discharge of combustibles from multiple pulverizer outlets. A further object is to provide a pulverizer throat construction of the type described which is characterized by its ability to permit operation of the pulverizer over an extended operating capacity range with a minimum-dribble of normally pulverizable material therethrough.

The Various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and'specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred. embodiment of my invention.

Of the drawings:

Fig. 1 is a sectional elevation of a pulverizer constructed in accordance with the present invention;

The pulverizer illustrated includes a cylindrical upper housing Ill and a lower section II supported on a foundation I2. The lower section II encloses the pulverizer gear drive which includes a horizontal pinion shaft, [3 arranged to drive a vertical drive shaft [4 axially arranged in the section H and the housing l0, The drive shaft ld extends upwardly through bearings ar ranged in a base plate I5" forming the top of the base section II. The upper housing I is detachably secured to the base plate i and en.- closes the grinding parts of the pulverizer which comprises a drive yoke ll of generally conical form keyed on the upper part of the drive shaft and an annular lower grinding ring ["8 sup ported on and dowelled to aflattened lower portion of the drive yoke. The upper face of the grinding ring is shaped to form a circular track for a row of rolling grinding elements 29-,- preferably balls of wear resistant ferrous alloy; The balls support a non-rotary upper grinding ring -2I-having a circular ball track formed in its lower face. An annular spider 22 mounted on the upper ring is provided with lugs 23 arranged in guides 29 on the inner wall of the housing Ill for preventing rotation, but permitting vertical movement of the spider 22 and upper grinding ring 2|. A resilient grinding pressure is exerted downwardly on the grinding parts by a number of coil springs 24 engaging the spider. 1 The material to be pulverized is supplie through a feed spout 25 to the inner side of the upper grinding ring 2| and the circular row of balls 28 and falls on the upper inclined surface of the yoke ll, being distributed throughout the grinding area by the rotation of the drive yoke and associated parts.- Due to the effect of centrifugal force the material flows outwardly be= tween the rings and balls, discharging therefrom at an oblique angle to the periphery of the -grind'-.

ping through the throat 32, and the gate sec-' tion 34, into the lower part of the pulverizer. The compartment 35 communicates with the grinding zone through a small opening 36 in the housing base plate below which a slidable gate 37 is mounted and manually operable through a rack and pinion system 38 to open and close the opening 36. The compartment 35 is periodically cleaned through a door 40.

ing elements depending upon their rotational carrier air from the wind box -30 passes into the housing iii through passages 3! into an annular space 39 in the housing it at the outer side of the drive yoke ll. The air stream then flows upwardly through a throat passage '32 formed between the outer side of the lower grinding ring 18 and an annular throat ring 33 mounted for radial adjustment on the inner side of the housing it]. A segmental portion of the outer throat wall is formed by a pivoted relief gate Sdvvhic'h swingsout to permit the passage of any large pieces of unpulverizable or foreign material, such as slate or tramp iron, iiito the lower portion of the housing IE3. At a position subsequent to the "relief gate 3 3, in the direction of rotation, the

base section H is provided with a pocket or compartment 35 for the collection of material drop- In the operation of the pulverizer illustrated,

the material to be pulverized is supplied to the inner side .of the grinding elements and is subjected to the pulverizing effects of the rings and balls during its outward fiow therethrough. As the pulverized material flows outwardly beyond the edge "of the lower ring [8 it is picked up by the stream of air ascending through the throat 32, with the material-laden air passing upwardly to the rotating classifier 26 which separates the coarse and 'fine particles, the coarse particle's being returned t6 the inner side of the ball row and the fine partieles delivered to the pulverizer outlet or outlets -21. The particles of materialno't picked up by the annular air stream, due to their excessive size or density, fall through the subj-acent part of the air throat'or through the relief gate section 3'4 into the air entrance areaat the outer side of the drive yoke H, and thence into the compartment 35.

When pulverizers of the type described are used in a direct firing system, the amount of air supplied to the pulverizer may be substantially proportional to the amount of 'coal pulverized or may be in some predetermined ratio with the amount of coal. In any event, the air velocity in the throat will vary over a wide range with changes in the pulverizer load. Accordingly, at low pulverizer loads, the air Velocity through the throat 32 may approach the minimum Velocity necessary to maintain in suspension the mass of pulverized materialoccurring at the discharge side of the grinding elements, and to lift the smaller particles of that material out of the grinding zone; The heavier particles of the suspended mass will tend to drop through the air stream and into the throat, either clogging a portion of the opening or falling through into the lewer part of the musing The amount of material dribbling through the throat 32 will or course vary with the velocity or the air passing therethrough and "at low pulverizer capacities the dribble may reach undesirable proportions. Such conditions may be aggravated by unequal distribution of air fiow "around the circumference of the throat wherby the flow velocities through one segment of the throat may be less than that through another segment; Under such conditions the minimum total air now to and through the pulverizer will be limited by the 'air velocity through that section of the throat having the lowest air flow, "otherwise the total loss b dribble through the one section of threat may be disproportionate to the total air flow to the pul- 'verizer. Such 'circumferentially unequal'air flows will also tend to cause an unequal sizing of the pulverized material delivered by the pulverizer and, when a plurality of pulverizer outlets 2? are provided, there maybe an inequality in the density of coal "and air mixture delivered through each outlet and an unequaluistribution 6f Coal and'air to each pulverizer putlet.

in the constructio'nand operation of air swept pulverizers'of the type described it has been customar to locate the air inlet 28 to the wind box 30 in a radial position with respect to the p'ulverizer, although the inlet may be tangential or at some intermediate position between radial and tangential Likewise, the throat opening has been formed to provide a substantially uniform pressure drop for air flow therethrough, as disclosed and claimed in Patent No. 2,378,681 of E. G. Bailey, et al., issued June 19, 1945. In the application referred to, lugs or crickets 4| are extended inwardly from the ring 33 to a position adjacent the rotating ring !8 whereby the velocity of air flow through each segment of the throat 32 between the crickets 4| is substantially uniform throughout the vertical height of the throat. However, it has been found that regardless of the position of the air inlet the air pressure at different positions in the wind box 30 will be re duced proportionately with its circumferential spacing from the air inlet 28. Thus, with the higher air pressure available in the vicinity of the air inlet, that portion of the throat 32 will receive a greater share of the air than a correspondingly equal circumferential portion of the throat in a comparatively lower wind box pressure area.

In accordance with the present invention the air flow, and thus the air velocity, leaving the upper end of the throat 32 and entering the pulverizing zone is equalized so that the air velocity leaving one circumferential portion of the throat is substantially equal to the velocity leaving any other equal portion of the throat. This is accomplished by the construction and installation of the throat ring 33 whereby the outer circumference of the ring 33 is coaxial with the axis of the pulverizer while the inner circumference of the ring-33, which forms the outer wall of the throat passage 34, is eccentric with respect to the rotative axes of the yoke I! and lower grinding ring H3. The crickets 41, previously referred to, are preferably cast integral with the ring 33 and their inwardly projecting sides are machined so as to be coaxial with the outer circumferenoe of that ring.

As shown particularly in Figs. 3 and 4, the inner circumference of the throat ring 33 is formed generally by the intersection of an upper inverted frusto-conical portion 33A and a lower frustoconical portion 33B. The conical surfaces are coaxial and eccentrically arranged with respect to the axial center line of the outer circumference of the ring 33. The surface of the upper conical portion 33A diverges upwardly and outwardly at an angle of approximately 45 from the plane of cone intersection while the lower surface 333 diverges downwardly and outwardly at an angle of approximately 75. Foruniformity in casting, the throat ring is cored so that the thickness of the walls of the ring is generally equal, except at l2 circumferentially spaced positions where internal bosses 42 are cast in the ringto provide metal for drilling and tapping to attach the ring to the housing ID by means of the stud bolts 43. A segment of the ring 33 is omitted as shown in Fig. 2 to provide space for the relief gate 34 previously described. Preferably the open ends of the ring adjoining the gate 34 are closed by welding plate sections 44 therein to prevent an accumulation of solid materials in the ring recess as might interfere with the operations of the relief gate.

Upon installation, the throat ring is positioned in the pulverizer so that the center of eccentricity, which is intersected by the coaxial centerlines of the conical surfaces 33A and 33B, is offset from the axis of rotation of the yoke IT on the radial centerline of and away from the air inlet 28.

above that of the upper circumferential corner of the grinding ring l8 at the side away from the air inlet. Accordingly the radial width of the throat passage 32 in the vicinity of the air inlet will be less than the corresponding width of the throat at a position on the opposite side of the pulverizer.

The radial throat width at intermediate circumferential positions will be proportionately graduated'between the minimum and maximum limits of throat width and will be equal at corresponding angular or circumferential positions on each side of the air inlet. Thus the throat width at positions and 270 from the air inlet in the direction of yoke rotation will be the same and correspond substantially to the average of the maximum and minimum throat widths.

As an example of throat ring eccentricity, the design area of free throat radial width for a medium capacity pulverizer with a concentric throat is 1%" and with an eccentric throat the amount of eccentricity is Thus, the radial width of the throat 32 between the grinding ring [8 and the throat ring 33 at the air inlet is 4%" and at a position 180 from the air inlet the radial throat width is 1%". At positions 90 on either side of the air inlet the throat width is 13- 5.

When such a pulverizer is operated at near rated capacities, static pressure readings taken at different circumferential positions in the wind box 33, such as at positions 45, 46 and 41 indicate static pressure drops for the air flow therethrough of approximately 1.3 inches water-gauge between positions 45 and 46 and approximately 1.6 inches water-gauge between positions 45 and 47. Due to the comparatively large area of the ports 3!, the static pressure drop due to the air flow therethrough is very low and of little consequence, so that the static pressure of the windbox 30 at circumferentially spaced positions'is correspondingly transmitted to the annular space 39 below the throat.

Advantageously, the described construction of the throat ring 33 provides a substantially uniform air flow velocity leaving the upper end of the throat passage 32 by compensating for the *unequal air pressure entering different circumferential segments of the lower portion of the throat passage.

I have found that the eccentric throat construction described will provide a substantially uniform distribution of air flow around the periphery of the lower grinding ring [8 and into the pulverized material discharging from the grinding elements. Such conditions are evidenced by static pressure readings at angularly spaced positions in the wind box 33 and throat passage 32 which indicate that the pressure and velocity of the air streams leaving the throat and entering the pulverizing zone are substantially uniform at all positions around the circumference of the pulverizer at each pulverizer operating capacity. Advantageously this throat construction permits an increased pulverizer capacity range without an excessive dribble of materials through the throat. The improved operation of the pulverizer is further evidenced by an improvement in the qualitative uniformity of the combustible mixture delivered to, theburners 7 aura-e54 through multiple puwerizer outlets as the result of a balanced air now through the pulverizing and classifying zones of the unit. Likewise, there is an essentially equal quantitative distribution of the coal and air mixture between the pulverizer discharge outlets, bothof which result from the "substantially uniform distribution of circumierential throat air now.

In the claims, the word air is intended to generically cover -any gaseous carrier medium suitable for removing pulverized material from the pulverizer in the manner described.-

l claim:-

is A- pulverizer comprising a closed casing,- a grinding member having an upper grinding surface, said member being mounted within the casing for rotation about a central vertical axis, for introducing material to be ground onto the upper grinding surface of the member, means cooperating with this grinding surface for grinding the material, an annular air chamber below said grinding member having a series of circumierentially spaced air inlet ports in the wall thereof, means for causing the pressure of the air delivered to said chamber to tgraduate downwa'rdly in value train a position adjaeent one circumferential portionof said chamber, and an annular throat ring having its central axis spaced from the central vertical axis of said rotary grinding member to define an annular throat between the grinding member and the throat ring with its radial width of circumferential opening gr'ad-uated in inverse relationship to the air pressure available in the subjacent air chamber to establish a substantially circumferentially uni-form 'air velocity upwardly through said throat for carr'y i-ng away pulverized material discharged from said grinding member.

2, :A pulverizer comprising a closed casing, a grinding member having an upper grinding sur- -f ace, said member being mounted within the easing for rotation about a central vertical axis, means forintroducing material to be ground onto the upper grinding surface of the member, means cooperating with this grinding surface for grind-- ing the material,- an annular air chamber below said grinding member,- a wind box encirclin said casing in communication with said annular air chamber through circumferentially spaced air portsandarranged to receive air from an inlet radial to the axis of said pulverizer, and an annular throat ring eccentrically arranged. with respect to said central vertical axis to define an air throat between said ring and the periphery of said grinding member, the eccentric throat spacing being graduated in radial width to compensate for the unequal air pressures maintained in said annular chamber for a circumferentially substantially uniform air flow upwardly through said throat to carry away pulverized material discharged by said rotary grinding member.

s. A pulverizer com risin a closed casing, a grindin member within the casing for rotation about a central vertical axis, a plurality of rolling grinding elements in contact with said rotary grinding member, means for introducing material to be ground between said rotary grinding mem bar and grinding elements, a wind box encircling said casing and having a series of circumferentially spaced air ports through the inner wall thereof in communication with the lower portion of said casing, said wind box decreasing in crosss'ectional area from a radial air inlet in one side to the opposite side said wind her, and a threat ring: iorming an annular throat above said air between the outer side oi said rotary grindin: member and the inner or said throat -riiig,seiidthroatring being arranged eccentri'cal ly about said rotary grinding elementwith the width of said throat greatestat a point opposite said air inlet and proportionately graduated to be smallest adjacent said air inlet to cause a cir' cumfereritially substantially uniform velocity of air through each se'gm'er'it of said throat,

4. A pulverizer comprising a closed casing, a grinding member within the casing for rotation about a central vertical a'xis, a plurality of rolling grinding eIements contact with said rotary 'g-rindihgmember, means for introducing material to be ground to the inside of said rotary grinding member and grinding elements, a Wind box encircling said casing arranged with a decreasing cross 'sectional area from an air inlet radially ar ranged with respect to said .pu-lverizer and having a series of ports through the inner wall of said wind box in communication with the lower portion of said casing, and an annular throat ring radially spaced from the periphery of said grind-- ing ring to define an annular air throattherebetween, the side of said air throat defined by the throat ring being eccentric with respect to said central vertical axis with the radial width of said air throat greatest at a point circumferentially opposite said air inlet and graduating equally on each semi-"circular side of said; throat circumference to its smallest radial width adjacent said air inlet to circmnferen-tia-lly equalize the air flow velocity upwardly past the discharge side of said grinding member.

5.- A pulverizer comprising a closed casing, a grinding ring mounted within the casing for rotation about a central vertical axis and having an upper grinding surface and an outwardly and downwardly flaring peripheral 'surface, means cooperating with said upper grinding surface to grind material therebetween, means for rotating said ring, a feeder arranged to deliver material to be ground to the inside of saidgrinding surface, an annular throat ring, having an outwardly and downwardly flaring inner surface radially spaced from the periphery of said grinding ring to define an annular air throat therebetween having a pair of downwardly diverging opposite sides, the diverging side of said throat defined by the throat ring being eccentric with respect to said central axis, said eccentricity of said throat ring being arranged to circumferential ly equalize the air flow leaving said annular throat by having the throat portion of greatest pressure drop of air flow through the throat corresponding with the highest static pressure of air entering the throat, crickets mounted on said throat ring and proportioned and arranged to subdivide said throat into a plurality of circumferntially adjacent passages each of substantially uniform cross-sectional flow area throughout its height, and means for introducing air upwardly through said throat to carr away air suspended pulverized material discharged by said grinding i 6. A pulverize'r com rising a casing enclosing a rotary grinding member, roiling grinding elements on said grinding member, means for delivering material to be pulverized to the inner side of said grindin elements, means for directing an annular stream or air upwardly past the outer side or said rinding member to sweep up pulver- 'iz'e-d material discharging therefrom including an annular throat ring cooperating with the outer periphery of said grinding member to define 'therebetween an annular air passage of substantially fixed new area, and means for maintain"- 9 ing a substantially uniformly distributed air velocity circumierentially through said throat which includes spacing the axis of said throat ring from the axis of said rotary grindin member to compensate by graduated pressure drop of air flow through said throat for the different pressures of the air entering circumferential portions of the annular air throat passage.

GRAHAM W. BICE.

REFERENCES CITED The following referencesare of record in the file of this patent:

Number 10 UNITED STATES PATENTS Name Date Hardgrove Sept. '7, 1937 Wood July 2, 1940 Hobbs Sept. 17, 1940 Schwartz Mar. 10, 1942 Bailey June 19, 1945 Ebersole June 21, 1949 

